The present invention relates to a disc device for recording data spirally on an optical disc, reproducing it therefrom or erasing it.
Image data storage/retrieval devices have recently developed. These devices photoelectrically convert image data such as a number of documents by one-dimensional optical scanning. Converted image data is stored in an image memory device. The data is retrieved from the image memory device and reproduced as a hard copy or soft copy as needed. Optical disc devices are recently used for the image data storage/retrieval devices of this type.
In a conventional optical disc device, an optical disc is used on which data is recorded in a spiral shape. An optical head which is linearly movable in the radial direction of the optical disc by a linear motor performs recording, reproducing and erasing. Among the conventional optical disc devices, a device is proposed in which a tracking differential signal is fed back to the linear motor in order to track data recorded in a spiral shape. However, in the optical disc device of this type, an error signal may then be supplied to the linear motor and accurate tracking cannot then be performed. Another device is proposed in which data is tracked by the movement of a movable lens within an optical head and the movement of an optical head driven by a linear motor. In the device of this type, the movable lens tracks data from the central position of the optical head to the allowable limit. If data is not sufficiently tracked, the optical head is then driven to cause the movable lens to be positioned at the center of the optical head. Then, the movable lens can track data again. However, in the device of this type, a step pulse is supplied to the linear motor and the device cannot be stably operated at the leading edge of the pulse.